1. Field of the Invention
This invention relates to a process for polymerizing organic isocyanates and is more particularly concerned with a process for trimerizing isocyanates in the presence of thermally activable catalysts and with novel catalysts therefor.
2. Description of the Prior Art
The polymerization of organic isocyanates and particularly polyisocyanates to form either cellular or solid polyisocyanurates is well known in the art. A large number and variety of trimerization catalysts have been disclosed in the prior art; see for example Saunders and Frisch Polyurethanes: Chemistry and Technology Part I, 1962, p 212, Interscience Publishers, New York, N.Y.
Quaternary ammonium salts and alkali metal salts of organic carboxylic acids have long been recognized as isocyanate trimerization catalysts. British Pat. No. 908,337 discloses both types of catalysts. U.S. Pat. No. 3,980,594 discloses particularly active quaternary ammonium salts.
U.S. Pat. No. 3,954,684 discloses effective trimerization catalyst combinations of tertiary amines with particular quaternary ammonium salts. Bis-quaternary ammonium salts have been disclosed as polyisocyanurate forming catalysts in U.S. Pat. No. 4,186,255.
In the art of isocyanate trimerization there has always been a need for delayed action or thermally activable catalysts. Generally speaking, the prior art catalysts are not useful in this regard because their properties have been directed at the opposite end of the scale, that is initiating the trimerization reaction at as low a temperature as possible.
It has now been discovered that a certain class of carboxylic acid salts, some of which are believed to be novel compounds, behave as thermally activable catalysts for trimerizing organic isocyanates. In contrast to prior art catalysts of the type referred to hereinbefore, the present catalysts can be premixed with the isocyanates at ambient temperature (about 20.degree. C.), and, in the absence of heat, are stable as such for literally hours before polymerization of the isocyanate initiates.